Combined single cell and single particle ICP-TQ-MS analysis to quantitatively evaluate the uptake and biotransformation of tellurium nanoparticles in bacteria.

Assessing the impact of nanoparticles in living systems implies a proper evaluation of their behaviour at single-cell level. Due to the small size of nanoparticles, their accumulation, transformation and location within single cells is challenging. In this work, the combination of single cell/single particle triple quadrupole inductively coupled plasma mass spectrometry (SC/SP-ICP-TQ-MS) analysis along with X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements has been applied to go deeper into the uptake and biotransformation of tellurium nanoparticles (TeNPs) in two bacterial model organisms, S. aureus and E. coli. The use of SC-ICP-TQ-MS enabled the individual introduction of bacterial cells where tellurium and phosphorous (as constitutive element) were monitored and detected at concentration levels down to femtogram (fg) per cell. S.aureus uptake of TeNPs was 0.5-1.9 fg Te cell-1 and 7-30 fg Te cell-1 in presence of 0.5 and 15 mg Te L-1 of TeNPs, respectively, whereas for E. coli, the amount of Te ranged from 0.08 to 0.88 fg Te cell-1 and from 2 to 36 fg Te cell-1 in presence of 0.5 and 15 mg Te L-1 of TeNPs, respectively. TEM and XRD analysis confirmed the occurrence of TeNPs biotransformation (from nanospheres to nanorods) as the nanoparticles were incorporated into both bacterial strains. Finally, SP-ICP-MS analysis after cell lysis was applied to determine the number of particles/rods per bacteria cell and to perform the dimensional characterization of the rod-shaped TeNPs. The results obtained clearly confirmed high cell-to-cell variability in terms of Te nanorods dimensions and TeNPs uptake. To the best of our knowledge, this is the first time that SC/SP-ICP-TQ-MS along with TEM and XRD analysis have been applied to investigate, quantitatively, nanoparticle uptake in bacterial cells and to estimate the dimensions of biogenic Te nanorods.